I tend to actually start buying stuff in November. I do most of my Christmas shopping online, so as long as I don't wait until the last 2 weeks, it doesn't really matter much.
I do kinda make mental note of ideas throughout the year. The problem is that my family tends to lean more towards the fun but practical when it comes to gifts, and if I come up with a good idea and buy it in say July, there is a non-trivial chance its intended recipient might end up buying it themselves before Christmas. There is generally an unspoken rule in my family that you arn't allowed to buy yourself any new "toys" in the November / December time frame unless you're damn sure it's not someones gift idea for you.